dual boot - Ubuntu won't reboot after resizing my Windows partition

I bought myself a new Acer AXC-603 computer a few months ago and, as I had been using Ubuntu for about five years, I've decided to configure my new machine in Dual Boot, keeping the majority of space for Windows, so that I can run a few games (even though it's far from being a gaming-computer). At first, the computer was set up with Windows 8. I was recommended to upgrade to Windows 10, once the initial Windows 8 configuration was done, which I did.

It's only after configuring Windows that I decided to install Ubuntu, but -not my best move- I only allocated about 18G to my main Ubuntu partition. It wasn't very long before I lacked space on it two days ago. I couldn't do the smallest thing without getting pop-up messages telling me the drive was full.

I've looked online to find out how I could simply resize my Windows partition in order to cut 20G from it and reallocate it to my Ubuntu partition. I must've done something wrong because right after resizsing my C: drive (after having defragmented it) Ubuntu won't boot. The GRUB screen appears, I select "ubuntu" (which I the first and default choice when I boot) and then, after a few seconds of Ubuntu's loading screen, everything goes blacks and I have to reboot.

I am currently on my LiveUSB. Here are some pictures of the situation, including from the Windows Disk Management (with which I cut off the 20G from the C:) and GParted.

Windows is installed on sda4, Ubuntu on my sda7. It's on the latter that I'd like to allocate the 19.53G of free space.

http://antoinemalette.com/documents/part2.jpg

http://antoinemalette.com/documents/part3.png

Thanks a million for your help.

Don't hesitate to ask if you need more informations. True to my habits, I must have forgotten to specify important things. You're great.

Greetings from Montréal,
Antoine

EDIT: I should also probably mention that I've started another thread (the same one, actually) on the French forums. There, I was given this advice:

Bonjour,

Tu bootes avec ton Live USB. Dans Gparted, tu désactives ta swap. Tu
déplaces ta partition sda6 vers la gauche. Tu agrandis ta partition
sda7 vers la gauche.

Ensuite, tu vérifies que les UUID sont correctes dans ton fstab. Tu
montes la partition sda7 et :

cat /media/xxxxxxxxxxxx/etc/fstab

(tu peux aussi afficher ton fstab en graphique) Puis :

sudo blkid

Si les UUID correspondent, tu peux rebooter.

A+

which translates into something like this:

Hi,

You boot with your LiveUSB. Using GParted, you desactivate your swap.
You move your sda6 partition to the left. You enlarge your sda7
partition to the left.

Then, you make sure your UUID are correct in your fstab. You mount the

sda7 partition and:

cat /media/xxxxxxxxxxxx/etc/fstab

(you can also show your fstab graphically.) And:

sudo blkid

If the UUID match, you may reboot.

I haven't done it yet, not being home before tonight, but will try it as soon as I get back. I must admit that I'll have to do some preliminary readings as I don't know what UUID and fstab are... Anyway, I'll let you guys know.